Dramatically speed up detailed heap snapshot generation.

src/profile-generator.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1012 matching lines @@
                            HeapEntry* parent,
                            String* reference_name,
                            Object* child);
   void SetElementReference(HeapObject* parent_obj,
                            HeapEntry* parent,
                            int index,
                            Object* child);
   void SetInternalReference(HeapObject* parent_obj,
                             HeapEntry* parent,
                             const char* reference_name,
-                            Object* child);
+                            Object* child,
+                            int field_offset = -1);
   void SetInternalReference(HeapObject* parent_obj,
                             HeapEntry* parent,
                             int index,
-                            Object* child);
+                            Object* child,
+                            int field_offset = -1);
   void SetHiddenReference(HeapObject* parent_obj,
                           HeapEntry* parent,
                           int index,
                           Object* child);
   void SetPropertyReference(HeapObject* parent_obj,
                             HeapEntry* parent,
                             String* reference_name,
-                            Object* child);
+                            Object* child,
+                            int field_offset = -1);
   void SetPropertyShortcutReference(HeapObject* parent_obj,
                                     HeapEntry* parent,
                                     String* reference_name,
                                     Object* child);
   void SetRootShortcutReference(Object* child);
   void SetRootGcRootsReference();
   void SetGcRootsReference(Object* child);
 
   HeapEntry* GetEntry(Object* obj);
 
   HeapSnapshot* snapshot_;
   HeapSnapshotsCollection* collection_;
   SnapshottingProgressReportingInterface* progress_;
-  // Used during references extraction to mark heap objects that
-  // are references via non-hidden properties.
-  HeapObjectsSet known_references_;
   SnapshotFillerInterface* filler_;
 
   static HeapObject* const kGcRootsObject;
 
   friend class IndexedReferencesExtractor;
   friend class RootsReferencesExtractor;
 
   DISALLOW_COPY_AND_ASSIGN(V8HeapExplorer);
 };
 
@@ skipping 127 matching lines @@
 };
 
 
 String* GetConstructorNameForHeapProfile(JSObject* object);
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 #endif  // V8_PROFILE_GENERATOR_H_